


errancy / inerrancy

by meowcosm



Category: Fire Emblem: Fuukasetsugetsu | Fire Emblem: Three Houses
Genre: Alien Biology, Bottom Seteth, Denial of Feelings, M/M, Male My Unit | Byleth, Male Solo, Masturbation, Monsterfucking, Pining, Sex Toys, Sexual Repression, Xenophilia
Language: English
Status: Completed
Published: 2020-05-08
Updated: 2020-05-08
Packaged: 2021-03-03 00:41:04
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,387
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/24065995
Author URL: https://archiveofourown.org/users/meowcosm/pseuds/meowcosm
Summary: Following Byleth's transfiguration at the chapel, Seteth is confronted with a powerful barrage of feelings, each more confusing than the last.He deals with this in the most reliable, if poorly-advised, fashion he knows of.-Written for the Fe3h Light Kinkmeme.
Relationships: My Unit | Byleth/Seteth
Comments: 6
Kudos: 65





	errancy / inerrancy

**Author's Note:**

> this is VERY HORNY and also kinda freaky. 
> 
> seteth has a sheathed cock and what's basically a vagina, though it's referred to as just his front hole + this is established as the male nabatean standard
> 
> also there's a brief blood mention late in the fic
> 
> enjoy!!!!

It had been, according to Seteth’s precise time-keeping, two weeks and three days since Byleth’s departure to the abandoned chapel on the monastery grounds. It too had been the same amount of time since Byleth’s transfiguration into some deified being, capable of wielding an even greater power than had been previously demonstrated in his hands, already remarkable in their ability to wield the Sword of the Creator without harm or detriment. 

Seteth, of course, had paid enraptured attention to all events following such. There was an abundance of unanswered questions- an overabundance, if Seteth was allowed his opinion on the matter. Still, it seemed hardly so- Rhea had disregarded the notion of its relevance to him almost entirely upon his questioning. Had asserted that he should- must, even- trust her on matters which seemed to be spiralling so wildly outside of present understanding. 

The prospect of renewing his blind trust had been an appealing one. He had much to deal with outside of the current stream of strange events; an academy would not administer itself, nor would Flayn protect or raise herself. These tasks could not be accomplished satisfactorily with the mind so heavily burdened by existential matters. It was best, then, to seek relief where it could be found. He could so easily delegate his worries to Rhea; let his mind be without weight or frustration. 

But it was Byleth. And though even the silent admittance that he had grown attached- fond, even- caught in his throat like a shameful confession, their continual entanglement had proved to be an enduring trend. One which gained even more meaning with Byleth’s transformation (if it was best given that name, for Seteth hardly understood what had occurred save for what he could intuit). A transformation which, if Seteth suspected wisely, had placed Byleth amongst the sole remaining members of the Nabateans. 

Characteristic shimmer-green hair, albeit paler than Seteth’s. Sharpened canines, designed for a diet that was no longer feasible in this changed world. Eyes that shimmered like dew on baby-grass.  _ Ears _ , changed only so slightly but in such a fashion that betrayed thoroughly non-human origins. 

He bore them all. So distinctively, but with little comprehension of what these changes entailed. Indeed, Seteth admitted shamefully to himself, it was only his constant fixation on them which ascribed these otherwise-slight physical traits such meaning. In concurrence with Rhea’s instruction to refrain from interference, but not solely motivated by it, Seteth had resigned himself to avoiding any attempt to influence Byleth’s thoughts on his new physiology. If he hoped for any positive developments in his role alongside Byleth, he could not make himself an intrusive presence. 

Still, he thought. Couldn’t stop himself thinking, to his nervous disgust. Thought about whether Byleth, like him, thanked the relative sharpness of his front teeth when it came to slicing through tougher cuts of meat, cursed it when anything requiring excessive chew became a fixture on the menu. If he craved, sometimes, rawness, blood trailing down his jaw as he bit deep into flesh. If Byleth could look himself in the mirror and call the face staring back at him his own, what with its alterations.

Worse than anything, though, were the carnal thoughts. Seteth felt quite depraved in the first place for ever allowing them to affect him, but no sooner than he questioned the dimensions of Byleth’s facial features had he summoned similar inquiries about his  _ other _ anatomy. His familiarity with the distinctions between human and Nabatean workings was extensive- the differences themselves not necessarily so, but with various distinctions which created a distinct system of reproduction. A partner with human anatomy had never been completely out of the question for Seteth, of course- if such a coupling was impossible, he would perhaps have less to worry about regarding Flayn. But he had grown used to the world revolving around human patterns, how they menstruated and conceived and birthed. Patterns distinct from his own, so much that it was a great task to not feel isolated amongst their constant acknowledgement. 

But. If he had already undergone such a potent transformation of his external features, Seteth could conclude with restrained confidence that he had been affected elsewhere. That he and Byleth were alone together.

Such a notion- well, it made Seteth’s mind wander. Sometimes idly, as he inevitably observed Byleth flit energetically between the students which flocked through each hallway and public space during the rest days and the space between lectures. Other times, actively, confined within the privacy of his own room. Where the thoughts, left unrestrained by the absence of any other presence, could overtake him, leaving him no choice but to use his hands for satisfaction. 

One finger, crooked and poised in preparation, hovered around Seteth’s hole. Lying, red and sensitive, in the dip behind the sheath of his cock, Seteth could feel its ring of muscle expand and contract in time with the even clenching and unclenching of his hips as he adjusted himself to lie comfortable on his back. He had long considered stiff unfulfillment down there an inevitable default, desire tamed like a de-stringed lyre. But solely in his anticipation, he felt his body’s willingness emerge, peaking even at the sheer possibility of touch. Slick was coating the tender insides of his thighs- his own fluids reminding him of just how deep such lechery ran through him. Withdrawing the one finger, if only briefly, Seteth brought his other hand to the area where it had lingered in waiting- far from alone, however. In his grip was clasped a large, teal-flecked object- rigid, broad and hooked distinctly at the base. Leaning forward on his headboard and against his pillows at the most suitable angle he could find, Seteth brought his other hand to grasp the flared base. It was a strange material, suiting such a strange object, one intended to bring sexual fulfillment to a population greatly limited in number. Resembling, to the best of its ability, the form of the Nabatean penetrative organ. 

If Seteth were to close his eyes, and ignore the lifelessness of the toy, he could imagine that this was Byleth’s pleasure poised over his slick hole. That it was Byleth above him, waiting for a chance to penetrate him, to insert himself far enough inside that he would become, if only for a brief moment in time, embedded inside Seteth. 

So he did, in the same moment that he brought the toy down into himself, its tip passing through Seteth in a fashion that brought him to an involuntary, wincing keen. Still, his body accepted it- a fact which Seteth was rather thankful for, as prior to the beginning of his experimentation he had been much tighter than was ideal for such an item. Enough that he had strained himself, almost to the point of injury, certainly enough for him to walk with great discomfort the next day- a matter of particular embarrassment when he’d met with Byleth the morning afterwards. 

He’d wondered, then, if Byleth had, too, experimented with his entrance. Not necessarily out of sexual desire- Seteth was not so brazen to assume Byleth shared anything close to mutual want for him, even if he should desire such a thing- but perhaps out of curiousity. Amongst the contrasts between Nabatean and human biology was the pronounced differentiation between human genders- Seteth did not presume that he knew, not exactly, but there was a reasonable chance that Byleth had not previously possessed a receptive place around the front of his pleasure. A  _ hole _ , to put it bluntly. One which became tender and slick during both arousal and mating, which was intended to receive penetration. Such was near-ubiquitous on Nabateans, but concentrated amongst humans, with Byleth having potentially lacked something like it before. 

How Byleth might touch himself, gentle, reconciling the difference of his new body with himself- Seteth could feel himself becoming wetter by the second at the simple thought of it. Aroused, too, to the point that there was little to be done about it but slip the toy further into himself, its width expanding at the base- an artistic embellishment of Nabatean anatomy, but one more ideal for pleasure. As taking it became a more labourious task, Seteth emitted a sound somewhere between a whine and a pleased groan, incipient on his lips as the tip dug deeper into his most sensitive reaches. With conscious effort, he angled it deeper, and let the pleasure overcome him. It was harder, then, for him to register his hesitant thoughts; that this was remarkably unbefitting behaviour for a man of his status, all directed towards someone who had brought him, at least on the surface level, an endless bounty of confusion. And as it became harder for him to muster up any hesitance, it too became harder for him to resist the cry which bubbled, nascent, at the back of his throat. 

_ Byleth _ . 

To say it with a toy in him, as he twisted his insides around it, was strange. But it was not unpleasant, and some hazily conscious part of Seteth’s mind grew guilty with the knowledge that this would be his impression of Byleth for much longer than he would like it to be. Especially when, once he closed his eyes and tried his earnest best to detach himself from the actions of his own hands, he could very well imagine Byleth inside of him. Byleth’s cock, unsheathed and aching, filling him- imagining it, Seteth pushed himself down onto the toy, rather than waiting for his conscious control over his hand to resume. Its new, greater deepness sent a renewed shudder through his body- even through the tears of overstimulation clouding the corners of his eyes, Seteth could see his own cock, erect. Dripping precome down onto his abdomen, slick and clear. 

_ Would Byleth’s cock look like that, now? _ Humans lacked sheaths, too, and spines. It was better for their coupling, Seteth had observed, and he had left it at that. But to think of Byleth, experimenting once more, hand coaxing his cock from its fleshy sheath to where he could touch its sensitivity and feel its throbbing warmth- how terrible it was, Seteth thought, and how  _ wonderful _ . 

Perhaps this would make it easier to let Byleth place all of his trust in Lady Rhea- Seteth could not, not in good conscience, give him advice on these matters now he had considered him in such a way. Perhaps he had already placed such confidence in the Archbishop, what with the limited curiousity he seemed to express about his new condition- then, Byleth had been a mercenary, used to a life of variability and change. He seemed to be coping remarkably well with the death of his father- to Seteth’s knowledge, the sole member of his family. 

Maybe that hope, that Byleth would need him- want him- was another aspect of Seteth’s perversion. His fixation was novel, preceded only by the deep debt Seteth owed him for Flayn’s safe return from the hands of the Death Knight. Something which Seteth had appreciated without the sudden urge to fuck himself deep on Byleth’s cock, and which Byleth would have done regardless of whether Seteth could offer him any carnal pleasures in return. 

He was, really, a man of considerable excellence and fortitude. Who acted with patient consideration, who had helped him so deeply- Seteth angled the toy inside him once more, pressing himself down on it til it felt as if he might be split apart by its considerable width, brushing up against the most sensitive part of his insides. Who might be just as frustrated as Seteth, deeply pent-up from the absence of pleasurable touch. 

_ Goddess _ , Seteth would let Byleth do anything to him. With the sureness that if he were truly being treated in such a fashion by Byleth, that Seteth would do nothing but fuck himself on his cock, writhing and moaning all the while- he was already not far off such a state, even solely through his own effort- Seteth sat up slightly, toy lingering in his hole. With his new position, he removed one of his hands from the intricate thing and brought it to the base of his cock, applying a single leisurely stroke before speeding up almost immediately. The friction was grating, with the only lubricant available his own fluids, but it did nothing but excite Seteth, his mind addled with physical sensation. Both hands in use, hips bucking wildly- thinking of one face, with only one name on his lips.

_ Byleth, Byleth, Byleth _ \- 

Something close to a burst of lightning magic passed through Seteth’s body, sending it into a writhing state. Though the toy lacked the ability to spend inside him as Byleth could (and, Seteth hoped, would want to), Seteth swore he felt the sensation of it- of being claimed, of receiving such pleasure. And it was that thought which pushed him off the edge, hurtling towards a blissful place of release, where the warm ache of being split open on his toy was negated by the rush of endorphins throughout his body. In the throes of his orgasm, Seteth bit down on his bottom lip, bringing ruby-red beads of blood to the surface of his skin as sharp canines pressed into the flesh- still, he barely noticed, focused as he was on stifling the violent cries of Byleth’s name which threatened to emerge from his mouth. 

Only when Seteth came back to himself, breath caught, did he notice the way he had spilled come on his jacket, or how streaks of red danced down from his bottom lip to the collar of the same garment. Even without a mirror, he suspected himself to look exactly as was logical- fucked out, and positively ruined. So thoroughly desperate at the thought of Byleth being inside of him that he had ruined his nicest clothes- which earned the title predominantly through their position as sole amongst the clothes he owned in the first place. 

He would have to call for laundry, and discreetly. Still, removing the toy from himself with a slick pop, he put that to the back of his mind, sighing as he did. It would be better, Seteth concluded, to take his rest now, before the deeper guilt he was sure to incur settled in. 

**Author's Note:**

> if you're a writer/want to submit a prompt come visit the light fe3h kinkmeme here! https://fe3h-kinkmeme-light.dreamwidth.org/
> 
> and if you're horny for setleth come follow me on twt @meowcosm where i post various things including but not restricted to horny seteth
> 
> most of all thank u for reading, leave a comment/kudos if you want!


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